Welcome to HCM.
You are suffering from irregular bleeding following taking seasonal birth control pill after birth of your daughter.It is due to hormonal imbalance caused by the pill.
There are several side effect in using birth control pill like irregular bleeding or spotting more likely in first 6 months, nausea, vomiting
, breast swelling & tenderness, headache, abdominal cramp
, mood swing
, psychological upset etc.
If heavy bleeding persists continuously,then do a USG scan to evaluate underlying pathology. Always consult to your doctor.